Heating installation for heating particulate raw materials

ABSTRACT

A succession of interconnected rotary kilns are independently heatable, with the burner of at least one kiln receiving an oxygen supply. The exhaust gases from the kilns are delivered to a pre-heating station for the raw material at the input end of the installation, and the combustion air is pre-heated at the output end by the heat released from the heated raw material.

States 3181M H 1 [111 3,712,600

Landthaler 1 Jan. 23, 1973 1 1 HEATING INSTALLATION FOR [56] References Cited HEATING PARTICULATE RAW UMTED STATES PATENTS MATERIALS H V 1,828,270 10/1931 Anderson "263/32 R [75] Inventor; Anton Landthal nAu u-ia 1,468,168 9/1923 Pike ..263/32R [73] Assignee: Veitscher Magnesitwerke Aktiengesellschaft, Vienna, Austria Primary Exammizrfllohn Camby Attorney-Kurt Kelman [521 File dz W J aili if, 1371 ABSTRACT [21] Appl. No.: 108,461

A succession of interconnected rotary kilns are independently heatable, with the burner of at least one [30] Foreign Apphcatmn Pnomy Data kiln receiving an oxygen supply. The exhaust gases Jan. 22,1970 Austria ..607 from the kilns are delivered to a pre heating tation p w for the raw material at the input end of the installa- 52 U.S. c|.....- ..263/32 R and the combustion air is tare-heated at the ouv [51] Int. Cl. ..F27b 7/02 p nd by h heat released from the heated raw [5 8] material.

Field of Search ..263/32, 36, 39

3 Claims, 5 Drawing Figures PATENTEDJAHZS ma 3.712.600

SHEET 1 BF 3 Fig. 1a

INnSN To R A Nrou uwu runes AGENT PATENTEDJAH 23 I975 SHEET 2 BF 3 INVENTOR Aura" LAMDTHH R 3V KM KWW PATENTEDJAH 23 I975 SHEET 3 [IF 3 INVENTO'K flNToN LA/vDnlH -EK 1 HEATING INSTALLATION FOR HEATING PARTICULATE RAW MATERIALS The present invention relates to improvements in heating installations for calcining or sintering preferably mineral raw materials, such as carbonates, oxides or hydroxides, including, for instance, magnesite in the production of calcined magnesia.

High-quality refractories are produced in such installations at high calcining temperatures which are obtained by enriching the combustion air with oxygen or by using pure oxygen as the combustion atmosphere. The oxygen or oxygen-enriched air is usually supplied to the heating station by means of an injection nozzle or jet. In such installations, the most economical use of the generated heat is of utmost commercial importance.

It is the primary object of this invention to solve the problem of heat economies most efficiently and to provide a heating installation of the indicated type which may be selectively operated at very high or at moderate temperatures, depending on the type of calcined material to be produced, while always maintaining the highest heat efficiency.

It has been proposed to provide a heating installation for calcining magnesite, for instance, which comprises two or more interconnected heating stations arranged in parallel and each provided with an independently operable burner, the raw material passing sequentially from an input end to an output end through the successive heating stations. One such known installation comprises a rotary kiln heated by a gas burner and a subsequent shaft or cupola furnace to which the magnesite is transferred from the rotary kiln with the admixture of a solid fuel, temperatures as high as 1,900 C being attained in the furnace. In this known installation, the exhaust gases from the furnace are passed through the rotary kiln. Since such gases are rich on nitrogen, they constitute ballast in the combustion process in the rotary kiln as far as heat economy is concerned.

A calcining installation for cement clinker has also been proposed wherein two interconnected rotary kilns are provided. In this installation, the exhaust gases of each kiln are collected and delivered to heat exchangers which serve as pre-heaters for the combustion gases of the kilns. While this arrangement avoids passing the exhaust gases from one kiln through the other kiln, the clinker is not pre-heated. Very high calcining temperatures cannot be reached in such an installation, such as have become desirable in more recently developed calcining processes.

The disadvantages of conventional heating installations for calcining particulate mineral raw materials have been overcome according to the invention by providing a first heating station including means for heating the station, a second heating station arranged in parallel with the first heating station and also including means for heating the station, which is independent of the heating means for the first station, and a connecting station for connecting the heating stations for transferring the raw material from the first to the second station. A pre-heating station for pre-heating the raw material is at the input end at the first station, and a cooling station is at the output end of the second station for cooling the heated raw material coming from the second heating station. The cooling station has an inlet for combustion air which is pre-heated in the cooling station by the heat released from the heated raw material. The exhaust gases of each heating station are collected and delivered to the pre-heating station, and means is provided for supplying oxygen to the heating means of at least one heating station. The heating means are selectively operable for heating selected heating station and the collected exhaust gases of the second station are selectively passed through or by the first station.

Preferably, each heating station consists of a rotary kiln, and a conduit delivers the pre-heated combustion air from the cooling station to the first heating station and by-passes the second heating station.

According to another preferred feature, the connection station comprises a stationary connecting head and the heating means for the first heating station is mounted in the connecting head. The conduit means for delivering the collected exhaust gases comprises a conduit selectively operable to receive the collected exhaust gases from the second heating station and to deliver the same to the pre-heating station. In some calcining operations, it will be useful to provide discharge means for the raw material at the connecting head.

The installation may include more than two heating stations, i.e., three stations, wherein the third station is included in the connecting station between the first and second heating station.

The above and other objects, advantages and features of the present invention will become more apparent from the following detailed description of certain now preferred embodiments, taken in conjunction with the accompanying drawing wherein FIG. I is a schematic side view of a two-station heating installation according to one embodiment of this invention;

FIG. la shows a temperature operating chart of the installation of FIG. 1;

FIG. 2 is a view similar to that of FIG. 1 of a modified two-station heating installation;

FIG. 2a shows a temperature operating chart of the installation of FIG. 2'; and a FIG. 3 is a view similar to that of FIG. 1 of a three station heating installation in accordance with another embodiment of the invention.

Referring now to the drawing, and first to FIG. 1, there is shown a heating installation comprising a preheater 1 for the raw material to be heated or calcined in the installation. The path of the raw material, which enters the installation at input end 3, is indicated by the chain-dotted line 2. After the raw material has been pre-heated, it passes into a rotary kiln constituting the first heating station 4, whence it is transferred through the connecting station 14, which is a fixed connecting head interposed between the first station 4 and the rotary kiln constituting the second heating station 5. The heated or calcined material passes from the station 5 into the cooling station 6 at the output end of the installation, where the hot material is cooled and the heat released from the material is used to preheat the combustion air being delivered into the cooling station through inlet 7. The pre-heated combustion air follows the path of broken line 11 through the combustion air conduit 9, into the first heating station 4 and by-passing the second heating station '5. Heating station 4 is independently heated by burner 8 whose exhaust gases follow the path of broken line 15 into the pre-heating station 1 where they are exhausted at 10.

The second heating station 5 is independently heated by burner 12 which receives oxygen or oxygen-enriched air through injection nozzle 13. The exhaust gases of the second heating station follow the path of broken line 15a into the connecting head 14 whence they are lead through exhaust gas conduit 16 into the pre-heating station 1.

As the chart of FIG. 1a shows, wherein the temperatures tC are entered along the ordinate and the path of the raw material through the installation flows along the abscissa, the highest temperatures are reached in the second heating station 5 because the oxygen-rich combustion air at burner 12 is not impeded by nitrogen-rich exhaust gases or diluted by the combustion air coming from the cooling station. n the other hand, high heating economies are obtained because the first heating station has its independent heating means 8 and receives pre-heated combustion air, the heating conditions in both stations being substantially independent of each other and independently adjustable.

Conventional control valves or dampers are mounted in the conduits 9 and 16 to make the draft therein adjustable, and the burners 8 and 12, as well as nozzle 13, are also adjustable, as is well known. None of these conventional adjustment or control means is shown to avoid encumbering the drawing with non-essential and well known details.

In the chart of FIG. la, the gas temperatures in the kilns are indicated in broken lines while the raw material temperature curve is shown in chain-dotted line.

The installation operates as follows:

The material to be heated or calcined is charged into the pre-heating station 1 where it is pre-heated by the exhaust gases coming from the first and second heating stations 4 and 5, i.e., the exhausted heat energy of both stations is utilized. The first heating station 4 is preferably heated with a fuel having a theoretically high flame temperature, for instance fuel oil. High temperatures are assured in the first heating station since it receives pre-heated combustion air from cooling station 6 through combustion air conduit 9, this conduit bypassing the second heating station 5 and thus preventing an admixture of exhaust gases thereto.

A suitable conveyor or transfer arrangement (not shown) moves the material heated in the first heating station 4 to the second heating station 5 where the highest calcining temperature is reached because of the use of an oxygen-enriched combustion air therein. The fuel used at burner 12 is again one having a high flame temperature, and oxygen or oxygen-enriched air is supplied through jet or nozzle 13. The exhaust gas from the second heating station 5 by-pass the first heating station and are delivered through conduit 16 directly to the pre-heating station 1. In this manner, the operation of the two rotary kilns is largely independent of each other, and the temperature in the first kiln 4 is not depressed by leading into it the exhaust gases from the second kiln 5, which are rich in nitrogen.

The calcined or sintered material is discharged from the second kiln 5 into the cooling station 6 wherein it transfers its heat to the combustion air entering the cooling station at 7, thus pre-heating the combustion air which is supplied to the first kiln 4. The cooling station will be so dimensioned that the material discharged therefrom may be transferred immediately to a further processing station while the pre-heated combustion air may be transferred in its entirety and at its highest temperature to first kiln 4. It is, of course, desirable to avoid heat losses.

The modified installation of FIG. 2 is similar to the installation of FIG. 1 and, to avoid redundancy in the description, like reference numerals in this figure indicate like parts operating in a like manner. It will'be noted that the conduits 9 and 16 are omitted in this modification. This may be accomplished, of course, simply by closing the valves in these conduits so that no combustion air may enter into conduit 9 and no exhaust gases may enter into conduit 16. In this way, the installation operates as though it had a single heating station consisting of kilns 4 and 5. The burner 8 remains in operation but the pre-heated combustion air from cooling station 6 passes (along the broken line path) consecutively through kiln 5 and then kiln 4.

As the chart of FIG. 2a shows, the highest temperature is reached in this installation at the end of the first heating station 4 while the temperature decreases steadily in the second heating station 5. In other words, the installation works with a shortened heating path of high intensity, i.e., only kiln 4 because the burner 12 and oxygen-supply nozzle 13 are disconnected so that the second kiln 5 is heated solely by the pre-heated combustion air coming from cooling station 6. Of course, if the heating requirements of the material so require, this operation may be reversed, i.e., the burner 8 may be turned off and the burner 12 may be operated to heat the second kiln instead of the first one. In this case, the material charged into the installation will be gradually heated in the first heating station, the temperature will reach a peak in the second heating station, and the hot material will be rapidly cooled in the cooling station.

A three-station installation embodying the principles of the present invention is illustrated in FIG. 3. This installation operates along the lines of the previously described embodiments, the connecting station herein including a third heating station.

Again, the material is charged into a pre-heating station 20 and follows the path indicated by chain-dotted line 2 through the installation. The first heating station is designated 22, followed by the third heating station 24 which connects the first heating station to the second heating station 26, each of the heating stations being constituted by a rotary kiln. Cooling station 28 is arranged at the discharge end of the installation to enable the heated material to be cooled, the heat of the cooled material being transferred to the combustion air charged into the cooling station at 30. Each heating station has a selectively operable burner 38, and selectively operable oxygen-supply nozzles 32, 34 and 36 may supply oxygen or oxygen-enriched air to the respective kilns.

As in the previous embodiments, means is again provided for collecting the exhaust gases of each heating station separately. For this purpose, exhaust gas conduits 40 and 42 are arranged to collect the exhaust gases from kilns 26 and 24, respectively, and to deliver these gases to respective zones in the pre-heating station 20 where they transfer their heat to the material being charged into the installation. The exhaust gases of the first kiln 22 are also collected at M and delivered into a third zone of the pre-heating station, as shown. The exhaust gases are removed from the pre-heating station through exhaust conduits by a blower 46, control vanes or valves 48 in the exhaust conduits regulating the draft so that no exhaust gases enter into the kilns with the pre-heated material.

The combustion air pre-heated in the cooling station 28 is removed therefrom by blower 50 and selectively delivered to nozzles 34 and 36 by operation of the control vanes or valves 52 in the supply conduits. If desired, the combustion air may be enriched by an admixture of oxygen. Similarly to the embodiment of FIG. 2, it is also possible to operate shut-off valves in conduits 40 and 42 so that the exhaust gases of the heating stations 26 and 24 do not by-pass the respectively preceding heating stations to be delivered directly to the p re-heating station but, instead, pass through these heating stations to combine with the exhaust gas in conduit 44.

Also, as in the previously described embodiments, the kilns are connected by connecting heads 54 and 56 through which the material is transferred from one station to the next and through which, if desired, the exhaust gases are removed. It may be useful to provide material discharge means at least at one of the connecting heads, preferably connecting head 56, so that partially calcined material may be removed at an intermediate point of the installation while the fully calcined or sintered material is transferred into the cooling station at the discharge end of the installation.

It will be obvious that an installation of the described type, which is preferably operated with rotary kilns for calcining or sintering such mineral materials as magnesite, dolomite, calcium oxide and the like, is not only very flexible for adaptation to different heating processes required for different starting materials and end products but enables heating temperatures of up to about 2,000 C to be-reached with the highest heating efficiency.

Iclaim:

l. A heating installation for heating a raw material, comprising 1. a first heating station including means for heating the station, said station having a raw material input end;

2. a second heating station arranged in series with the first heating station and including means for heating the station, said station having a heated raw material output end,

a. the heating means for the second station being independent of the heating means for the first station;

3. a connecting station for connecting the first and second heating stations for transferring the raw material from the first to the second station,

a. the connecting station including a third heating station including selectively operable means for heating the station;

4. a pre-heating station at the input end for pre-heating the raw material;

5. a cooling station at the output end for cooling the heated raw material coming from the second heating station;

6. an inlet for combustion air at the cooling station for delivering combustion air to the cooling station,

a. the combustion air being pre-heated in the cooling station by the heat released from the heated raw material;

. means for collecting the exhaust gases of each of said heating stations;

. conduit means for delivering the collected exhaust gases to the pre-heating station;

. selectively operable means for supplying oxygen to the heating means of at least one of said heating stations,

a. the heating means being selectively operable for heating selected ones of the heating stations, and

b. the collected exhaust gases of the second station being selectively passed through or by the first station; and

10. a conduit means for selectively delivering the pre-heated combustion air from the cooling station to the third or first heating station and by-passing the second heating station.

2. A heating installation for heating a raw material,

comprising 1. a first rotary kiln including means for heating the kiln, the kiln having a raw material input end;

2. a second rotary kiln arranged in series with the first kiln and including means for heating the kiln, the kiln having a heated raw material output end, a. the heating means for the second kiln being independent of the heating means for the first kiln;

3. a pre-heating station upstream of the input end for pre-heating the raw material;

. a cooling station downstream of the output end for cooling the heated raw material coming from the second rotary kiln;

. connecting station respectively connecting the pre-heating station to the first rotary kiln, the first and second rotary kilns, and the second rotary kiln to the cooling station for transferring the raw material therebetween;

6. an inlet for combustion air at the cooling station for delivering combustion air to the cooling station,

a. the combustion air being pre-heated in the cooling station by the heat released from the heated raw material;

7. individual means for collecting the exhaust gases of each of the rotary kilns and for directly delivering the exhaust gases to the pre-heating station;

8. means for collecting the air pre-heated in the cooling station and for delivering the pre-heated air as combustion air to the heating means of the first rotary kiln; and

9. means independent of the pre-heated air collecting and delivering means for supplying oxygen-enriched air to the heating means of the second rotary kiln.

3. The heating installation of claim 2, wherein the oxygen-enriched air supplying means is selectively operable, the heating means are selectively operable for heating selected ones of the rotary kilns, and the collected exhaust gases of the second rotary kiln are selectively passed through or by the first rotary kiln. 

1. A heating installation for heating a raw material, comprising
 1. a first heating station including means for heating the station, said station having a raw material input end;
 2. a second heating station arranged in series with the first heating station and including means for heating the station, said station having a heated raw material output end, a. the heating means for the second station being independent of the heating means for the first station;
 3. a connecting station for connecting the first and second heating stations for transferring the raw material from the first to the second station, a. the connecting station including a third heating station including selectively operable means for heating the station;
 4. a pre-heating station at the input end for pre-heating the raw material;
 5. a cooling station at the output end for cooling the heated raw material coming from the second heating station;
 6. an inlet for combustion air at the cooling station for delivering combustion air to the cooling station, a. the combustion air being pre-heated in the cooling station by the heat released from the heated raw material;
 7. means for collecting the exhaust gases of each of said heating stations;
 8. conduit means for delivering the collected exhaust gases to the pre-heating station;
 9. selectively operable means for supplying oxygen to the heating means of at least one of said heating stations, a. the heating means being selectively operable for heating selected ones of the heating stations, and b. the collected exhaust gases of the second station being selectively passed through or by the first station; and
 10. a conduit means for selectively delivering the pre-heated combustion air from the cooling station to the third or first heating station and by-passing the second heating station.
 2. a second heating station arranged in series with the first heating station and including means for heating the station, said station having a heated raw material output end, a. the heating means for the second station being independent of the heating means for the first station;
 2. a second rotary kiln arranged in series with the first kiln and including means for heating the kiln, the kiln having a heated raw material output end, a. the heating means for the second kiln being independent of the heating means for the first kiln;
 2. A heating installation for heating a raw material, comprising
 3. The heating installation of claim 2, wherein the oxygen-enriched air supplying means is selectively operable, the heating means are selectively operable for heating selected ones of the rotary kilns, and the collected exhaust gases of the second rotary kiln are selectively passed through or by the first rotary kiln.
 3. a pre-heating station upstream of the input end for pre-heating the raw material;
 3. a connecting station for connecting the first and second heating stations for transferring the raw material from the first to the second station, a. the connecting station including a third heating station including selectively operable means for heating the station;
 4. a cooling station downstream of the output end for cooling the heated raw material coming from the second rotary kiln;
 4. a pre-heating station at the input end for pre-heating the raw material;
 5. a cooling station at the output end for cooling the heated raw material coming from the second heating station;
 5. connecting station respectively connecting the pre-heating station to the first rotary kiln, the first and second rotary kilns, and the second rotary kiln to the cooling station for transferring the raw material therebetween;
 6. an inlet for combustion air at the cooling station for delivering combustion air to the cooling station, a. the combustion air being pre-heated in the cooling station by the heat released from the heated raw material;
 6. an inlet for combustion air at the cooling station for delivering combustion air to the cooling station, a. the combustion air being pre-heated in the cooling station by the heat released from the heated raw material;
 7. means for collecting the exhaust gases of each of said heating stations;
 7. individual means for collecting the exhaust gases of each of the rotary kilns and for directly delivering the exhaust gases to the pre-heating station;
 8. means for collecting the air pre-heated in the cooling station and for delivering the pre-heated air as combustion air to the heating means of the first rotary kiln; and
 8. conduit means for delivering the collected exhaust gases to the pre-heating station;
 9. selectively operable means for supplying oxygen to the heating means of at least one of said heating stations, a. the heating means being selectively operable for heating selected ones of the heating stations, and b. the collected exhaust gases of the second station being selectively passed through or by the first station; and
 9. means independent of the pre-heated air collecting And delivering means for supplying oxygen-enriched air to the heating means of the second rotary kiln.
 10. a conduit means for selectively delivering the pre-heated combustion air from the cooling station to the third or first heating station and by-passing the second heating station. 